Self-exciting sensors are used in many applications. Self-exciting sensors internally generate an excitation signal that is received by the sensor itself. The sensor then measures variations in the excitation signal to sense certain physical parameters. For example, an optically coupled sensor is utilized in sensing a relative position of an automotive steering wheel.
Some automotive vehicles incorporate a control system for carrying out given control in response to a steering angle calculated from the relative position. The typical optics-based position sensor includes an exciter ring concentrically surrounding a steering wheel shaft. Optical pulses are generated in accordance with rotation of the steering wheel when the driver operates the steering wheel. Information on the steering angle of the vehicle is obtained by means of a counter which counts signal pulses based on the optical signal pulses.
However, in the event that a failure occurs in the sensor itself, it is impossible to carry out proper control in response to the steering angle. Typically, a sensor is coupled to the position sensor to detect any failures associated with the sensor itself. However, it is desirable to eliminate such cost and unreliability associated with an additional sensor or input to a control logic when detecting a failure associated with the position sensor, or any other similar self-exciting sensor.